The Clod Ensemble are a shape-shifting, genre-straddling, media-mixing, experimental, experiential, project-based performance group. What does that mean in practice? One result is Under Glass, a 45-minute show directed by Suzy Willson that is currently running in an old Victorian warehouse. Several times a day, spectators (in groups of about 30) are ushered around the gloomy interior to witness a kind of living exhibition.

From the shadows all around, a series of people, encased in their own transparent cabinets, are intermittently illuminated. There is a man at his desk, pasting notes to the wall and adjusting his Anglepoise lamp as if everything were fine, though he can't even stand up straight inside his cramped glass box. A couple in a flat circular case grope like blind nestlings. One woman twists like a homunculus in a specimen jar; another squishes her belly against the side of her cabinet until it looks like a fleshy mollusc in an aquarium; another talks into a telephone - scraps of poetry (written by Alice Oswald) that evoke fear and disturbance beneath a surface of precarious normality. Throughout, Paul Clark's score - melancholy strings, Morse code blips, chimes, rumbles and, unexpectedly, a burst of shouty rock - creates broody, unstable moods, while Hansjorg Schmidt's lighting makes the scenes feel like fragments of a dream.

What does it amount to? That rather depends on you: its imagery is dramatic but it is not drama; figures move, but it is not dance. I found it beautifully produced, but too intangible. At its best, though, it generated a powerful melancholy - each person utterly alone within their own little patch of world. At the end, too, when they turn inside their cabinets to look at us, applauding from within our own patch of light, it is as if we are the lonely weirdos, not them. Now that was spooky.